Anti-glare substrates with low sparkle, doi and transmission haze

ABSTRACT

Embodiments of anti-glare substrates and articles including the same are disclosed. In one or more embodiments, the anti-glares substrate includes a textured surface with a plurality of features having an average cross-sectional dimension of about 30 micrometers or less. The substrate or article exhibits a transmission haze of 10% or less, a PPDr of about 7% or less or 6% or less, and a DOI of about 80 or less. Method for forming the anti-glare substrates are also disclosed and include etching a surface of a substrate with an etchant having low water solubility to provide an etched surface, and removing a portion of the etched surface. The method includes generating a plurality of insoluble crystals (e.g., any one or more of K2SiF6 and K3AlF6) on the surface while etching the surface. The etchant may include a potassium salt, an organic solvent and a fluoride containing acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/506,503filed on Feb. 23, 2017, which is a national stage entry of InternationalPatent Application Serial No. PCT/US15/48510 filed on Sep. 4, 2015,which claims the benefit of priority under 35 U.S.C. § 119 of U.S.Provisional Application Ser. No. 62/047,254 filed on Sep. 8, 2014 thecontent of each of which is relied upon and incorporated herein byreference in its entirety.

BACKGROUND

The disclosure relates to substrates exhibiting anti-glare propertiesand more particularly to substrates exhibiting low sparkle, lowdistinctiveness of image (DOI), and low transmission haze.

Advances in consumer electronic technology has necessitated improvementsin various cover substrate properties. One such area for improvement isanti-glare surfaces for consumer electronic devices such as smart(mobile) phones, tablets, electronic readers, displays and TVs.

Known anti-glare surfaces often have textured surfaces that are formedby forming crystals on the surface of the substrate and etching portionsof the substrate not covered by the crystals. In some instances,hydrofluoric acid (HF), ammonium bifluoride (NH₄HF₂), propylene glycol(PG), and a mineral acids (such as sulfuric acid, H₂SO₄) are utilized toform such anti-glare surfaces on glass substrates.

For consumer electronic applications, known anti-glare surfaces canexhibit sparkle (or a grainy appearance) at low transmittance hazelevels (e.g., about 10% or less). Display “sparkle” is a phenomenon thatcan occur when anti-glare or light scattering surfaces are incorporatedinto a display system. Sparkle is associated with a very fine grainyappearance that can appear to have a shift in the pattern of the grainswith changing viewing angle of the display. This type of sparkle isobserved when pixelated displays such as LCDs are viewed through anantiglare surface. Such sparkle is of a different type and origin from“sparkle” or “speckle” that has been observed and characterized inprojection or laser systems

As displays exhibit higher definition and more pixels are assembled athigher densities, the reduction of sparkle becomes more important.Accordingly, there is a need for anti-glare surfaces that exhibit lowsparkle, while still exhibiting low DOI and low transmission haze.

SUMMARY

A first aspect of this disclosure pertains to a method of forming anantiglare surface that includes etching a portion of a surface of asubstrate with an etchant to provide an etched surface, and removing aportion of the etched surface to provide the anti-glare surface. Theresulting substrate with the anti-glare surface exhibits a transmissionhaze 10% or less, and a PPDr of about 6% or less, and the anti-glaresurface exhibits a DOI of about 80 or less. The resulting the anti-glaresurface may include a textured surface with plurality of concavefeatures having an opening facing outwardly from the surface. Theopening may have an average cross-sectional dimension of about 30micrometers or less.

In one or more embodiments, the method includes generating a pluralityof insoluble crystals on the surface while etching a portion of thesurface with the etchant (which may be applied by spraying). The etchantmay exhibit a water solubility of about 50 g/100 g water or less. Insome instances, the insoluble crystals include potassium and may includeany one or more of K₂SiF₆ and K₃AlF₆. In some other instances, theinsoluble crystals exhibit a water solubility of less than about 10g/100 g water.

In one or more embodiments, removing a portion of the etched surfaceincludes removing a thickness up to about 100 micrometers of the surface(e.g., from about 40 micrometers to about 100 micrometers). Thethickness may be removed by exposing the surface to a chemical polishingsolution. In some instances, the etchant is removed prior to removingthe portion of the etched surface.

In one or more embodiments, the etchant includes a potassium salt, whichmay be present in an amount in the range from about 1 wt % to about 20wt % or from about 5 wt % to about 15 wt %. The potassium salt mayinclude any one or more of potassium chloride (KCl), potassium nitrate(KNO₃), potassium sulfate (K₂SO₄) and potassium acetate. The etchant mayalso include an organic solvent and a fluoride containing acid. Theorganic solvent may be present in an amount in the range from about 0 wt% to about 40 wt % and can include a water miscible organic solvent. Inone or more embodiments, the fluoride containing acid is present in anamount in the range from about 0.5 wt % to about 6 wt % and may includeany one or more of hydrofluoric acid (HF) and ammonium bifluoride(NH₄HF₂). In some examples, the is substantially free of ammonium salt.In other examples, the etchant may include ammonium fluoride (NH₄F), aninsoluble particle, a surfactant or a combination thereof.

The method may utilize a substrate that may be amorphous or crystalline.Examples of suitable amorphous substrates include glasses such as sodalime glass, alkali aluminosilicate glass, alkali containing borosilicateglass and alkali aluminoborosilicate glass. In some instances, the glassmay be chemically strengthened and may include a compressive stress (CS)layer with a surface CS of at least 250 MPa extending within thechemically strengthened glass from a surface of the glass to a depth oflayer (DOL) of at about 10 μm or greater.

A second aspect of this disclosure pertains to a substrate that exhibitslow sparkle (in terms of low pixel power deviation reference or PPDr),low DOI and low transmission haze. In one or more embodiments, thesubstrate includes an anti-glare surface that includes a texturedsurface having features having an average cross-sectional dimension ofabout 30 micrometers (μm) or less. In some instances, the featuresinclude a Rsk value in the range from about 1 to about −1. In someembodiments, the article (or the textured surface thereof) exhibits atransmission haze of 10% or less, a PPDr of less than about 7% (or about6% or less) and a DOI of about 80 or less.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed descriptionwhich follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understanding the natureand character of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiment(s), and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view illustration of one embodiment;

FIG. 2A is a process flow diagram showing a method of forming thetextured surface of one or more embodiments;

FIG. 2B is a process flow diagram shown a known method of forming knowntextured surfaces;

FIG. 3 is a graph showing the PPDr and DOI measurements achievable at atransmission haze of 10% of one or more embodiments;

FIG. 4 is a graph showing the PPDr and DOI measurements achievable at atransmission haze of 10%;

FIG. 5 is an image of the etched surface of Example 1, taken by NikonOptical Microscope, at 200× magnification;

FIG. 6 is an image of the textured surface of Example 1, taken by NikonOptical Microscope, at 200× magnification; and

FIG. 7 is a graph showing the calculated PPDr and DOI measurements ofExample 6 and comparative substrates.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiment(s) of thisdisclosure

A first aspect of this disclosure pertains to a substrate exhibitinganti-glare properties and articles including the same. Specifically, theanti-glare substrate exhibits a transmission haze 10% or less, a PPDr ofabout 6% or less and a DOI of about 80 or less, as measured on thesurface including the anti-glare surface (or textured or roughenedsurface).

Referring to FIG. 1, in one or more embodiments, the substrate 100includes opposing major surfaces 112, 114 and opposing minor surfaces116, 118. In some embodiments, at least one surface (e.g., a majorsurface) includes a texture (referred to herein as a textured surface120) with a plurality of features 122. The texture may extend across aportion of the surface, the entire surface or on more than one surface.The texture may be referred to as roughened. The features 120 may bedescribed as concave shape extending into the substrate from the surfacewith an opening at the surface, facing outwardly from the surface, asshown in FIG. 1.

Unless otherwise stated, the anti-glare performance of the substrate 100in terms of DOI is measured on the surface with the texture or theplurality of features 122, in reflected mode (i.e., without taking intoaccount the other surfaces of the substrate). PPDr and transmission hazeperformance is in terms of the entire substrate, since these values aremeasured in the transmitted mode.

In one or more embodiments, features of the textured surface 120 mayhave an average cross-sectional dimension of about 30 micrometers orless. The average cross-sectional dimension may be measured at theopening on the surface. In some embodiments, the features 122 have anaverage cross-sectional dimension in the range from about 10 micrometersto about 30 micrometers, from about 10 micrometers to about 28micrometers, from about 10 micrometers to about 26 micrometers, fromabout 10 micrometers to about 24 micrometers, from about 10 micrometersto about 22 micrometers, from about 10 micrometers to about 20micrometers, from about 12 micrometers to about 30 micrometers, fromabout 14 micrometers to about 30 micrometers, from about 16 micrometersto about 30 micrometers, from about 18 micrometers to about 30micrometers, from about 20 micrometers to about 30 micrometers, fromabout 15 micrometers to about 25 micrometers, from about 17 micrometersto about 25 micrometers, from about 20 micrometers to about 25micrometers, or from about 20 micrometers to about 22 micrometers. Asused herein, the term “longest cross-sectional dimension” refers to thelongest single dimension of the features. Thus, to clarify, when afeature is circular, the longest cross-sectional dimension is itsdiameter; when a feature is oval-shaped, the longest cross-sectionaldimension is the longest diameter of the oval; and when a feature isirregularly-shaped, the longest cross-sectional dimension is the linebetween the two farthest opposing points on its perimeter. The term“average” when used with “longest cross-sectional dimension” includesthe average of the measured longest cross-sectional dimensions of least20 different features on the same sample.

In one or more embodiments, the substrate exhibits low sparkle which maybe characterized by a pixel power deviation reference or PPDr of about7% or less, about 6.5% or less, about 6% or less, about 5.5% or less,about 5% or less, about 4.5% or less, about 4% or less, about 3.5% orless, or about 3% or less. As used herein, the terms “pixel powerdeviation referenced” and “PPDr” refer to the quantitative measurementfor display sparkle. Unless otherwise specified, PPDr is measured usinga display arrangement that includes an edge-lit LCD screen (twistednematic LCD) having a native sub-pixel pitch of 60 μm×180 μm and asub-pixel opening window size of about 44 μm×about 142 μm. The frontsurface of the LCD screen had a glossy, anti-reflection type linearpolarizer film. To determine PPDr of a display system or an anti-glaresurface that forms a portion of a display system, a screen is placed inthe focal region of an “eye-simulator” camera, which approximates theparameters of the eye of a human observer. As such, the camera systemincludes an aperture (or “pupil aperture”) that is inserted into theoptical path to adjust the collection angle of light, and thusapproximate the aperture of the pupil of the human eye. In the PPDrmeasurements described herein, the iris diaphragm subtends an angle of18 milliradians.

PPDr measurements can be distinguished from PPD measurements used tocharacterize known anti-glare surfaces. PPDr includes a normalizedstandard deviation of pixel power and is more fully described in J.Gollier et al., “Display sparkle measurement and human response,”SIDSymposium of Technical Papers 44, No. 1, 295-297 (2013). To calculatethe PPD contribution from the display alone, the pixel power variationthe emissive display without the anti-glare surface is removed toprovide a PPDr measurement (denoting a referenced measurement).Generally, a first image of the bare display is taken and used as areference for the image taken with the test sample containing theanti-glare surface. The boundaries between adjacent pixels arecalculated by summing the lines then rows in the image and determiningthe minima. For very noisy images the locations of the integratedregions may need to be estimated using the knowledge that the pixelpitch in the emissive display is constant. The background countsobserved in the dark regions between the pixels is subtracted from theimage to remove camera dark counts or other scattered light within thedisplay. Total power within each pixel is then integrated and normalizedby dividing by the pixel powers from the reference image. The standarddeviation of the distribution of pixel powers is then calculated to givethe PPDr value.

More specifically, in measuring PPDr, a uniform green patch of an LCDpixel is used as a source. Only the green sub-pixels are illuminatedwith a minimum measurement area of about 20×20 LCD pixels. Test images(T_(ij)) and reference images (R_(ij)) are acquired. The reference imageremoves non-uniformity in source intensity distribution. The image ofthe LCD pixels as viewed through the iris is collected by a CCD(charge-coupled device) camera having at least about 20 CCD pixels perLCD pixel. Background values (bg) are also determined to removecontributions from stray light and dark counts. The PPDr value isdetermined by equations (1) and (2).

A _(ij)=(T _(ij) −bg)/(R _(ij) −bg)  (1)

PPDr=St. Dev.[A _(ij)]*100  (2)

PPDr measurements may be taken at 0° and at 90°. PPDr values refer tothe mathematical average of these measurements.

In some embodiments, the anti-glare surface exhibits a 20° distinctnessof image (DOI) of less than about 85. In some embodiments, the DOI ofthe anti-glare surface is less than about 80, less than about 60 or lessthan about 40. As used herein, the term “distinctness of image” isdefined by method A of ASTM procedure D5767 (ASTM 5767), entitled“Standard Test Methods for Instrumental Measurements ofDistinctness-of-Image Gloss of Coating Surfaces,” the contents of whichare incorporated herein by reference in their entirety. In accordancewith method A of ASTM 5767, substrate reflectance factor measurementsare made on the anti-glare surface at the specular viewing angle and atan angle slightly off the specular viewing angle. The values obtainedfrom these measurements are combined to provide a DOI value. Inparticular, DOI is calculated according to the equation

$\begin{matrix}{{{DOI} = {\left\lbrack {1 - \frac{Ros}{Rs}} \right\rbrack \times 100}},} & (3)\end{matrix}$

where Ros is the relative reflection intensity average between 0.2° and0.4 away from the specular reflection direction, and Rs is the relativereflection intensity average in the specular direction (between +0.05°and −0.05°, centered around the specular reflection direction). If theinput light source angle is +20° from the sample surface normal (as itis throughout this disclosure), and the surface normal to the sample istaken as 0°, then the measurement of specular reflected light Rs istaken as an average in the range of about −19.95° to −20.05°, and Ros istaken as the average reflected intensity in the range of about −20.2° to−20.4° (or from −19.6° to −19.8°, or an average of both of these tworanges). As used herein, DOI values should be directly interpreted asspecifying a target ratio of Ros/Rs as defined herein. In someembodiments, the anti-glare surface has a reflected scattering profilesuch that >95% of the reflected optical power is contained within a coneof +/−10°, where the cone is centered around the specular reflectiondirection for any input angle.

In some embodiments, the anti-glare surface described herein has atransmission haze value of about 10% or less. In some embodiments, thetransmission haze of the transparent glass sheet about 8% or less, about6% or less or about 5% or less. As used herein, the terms “transmissionhaze” and “haze” refer to the percentage of transmitted light scatteredoutside an angular cone of about ±2.5° in accordance with ASTM procedureD1003. For an optically smooth surface, transmission haze is generallyclose to zero.

In some embodiments, the anti-glare surface exhibits an RMS roughness ofabout 200 nanometers (nm) or greater. In some embodiments, theanti-glare surface exhibits a RMS roughness value of about 210nanometers or greater, about 220 nanometers or greater, about 230nanometers or greater, about 240 nanometers or greater, about 250nanometers or greater, about 300 nanometers or greater, about 350nanometers or greater, about 400 nanometers or greater, about 450nanometers or greater or about 500 nanometers or greater.

In some instances, the anti-glare surface exhibits a skewness (Rsk)value in the range from about −1 to about for from about −0.5 to about0.5. Without being bound by theory, surfaces with a Rsk value of greaterthan 1 are less durable in terms of scratch resistance than surfaceswith a Rsk value of about 1 or less and surfaces with a Rsk value ofless than about −1 may have reduced strength than surfaces having an Rskvalue of about −1 or greater.

The substrate used to form the anti-glare surface may be inorganic andmay include an amorphous substrate, a crystalline substrate or acombination thereof. In one or more embodiments, the substrate may beamorphous and may include glass, which may be strengthened ornon-strengthened. Examples of suitable glass include soda lime glass,alkali aluminosilicate glass, alkali containing borosilicate glass andalkali aluminoborosilicate glass. In one or more alternativeembodiments, the substrate may include crystalline substrates such asglass ceramic substrates (which may be strengthened or non-strengthened)or may include a single crystal structure, such as sapphire. In one ormore specific embodiments, the substrate includes an amorphous base(e.g., glass) and a crystalline cladding (e.g., sapphire layer, apolycrystalline alumina layer and/or or a spinel (MgAl₂O₄) layer).

The substrate may be substantially planar or sheet-like, although otherembodiments may utilize a curved or otherwise shaped or sculptedsubstrate. The substrate may be substantially optically clear,transparent and free from light scattering. In such embodiments, thesubstrate may exhibit an average light transmission over the opticalwavelength regime of about 85% or greater, about 86% or greater, about87% or greater, about 88% or greater, about 89% or greater, about 90% orgreater, about 91% or greater or about 92% or greater. In one or morealternative embodiments, the substrate may be opaque or exhibit anaverage light transmission over the optical wavelength regime of lessthan about 10%, less than about 9%, less than about 8%, less than about7%, less than about 6%, less than about 5%, less than about 4%, lessthan about 3%, less than about 2%, less than about 1%, or less thanabout 0%. The substrate may optionally exhibit a color, such as white,black, red, blue, green, yellow, orange etc.

Additionally or alternatively, the physical thickness of the substratemay vary along one or more of its dimensions for aesthetic and/orfunctional reasons. For example, the edges of the substrate may bethicker as compared to more central regions of the substrate 100. Thelength, width and physical thickness dimensions of the substrate mayalso vary according to the application or use.

The substrate may be provided using a variety of different processes.For instance, where the substrate includes an amorphous substrate suchas glass, various forming methods can include float glass processes anddown-draw processes such as fusion draw and slot draw.

Once formed, a substrate may be strengthened to form a strengthenedsubstrate. As used herein, the term “strengthened substrate” may referto a substrate that has been chemically strengthened, for examplethrough ion-exchange of larger ions for smaller ions in the surface ofthe substrate. However, other strengthening methods known in the art,such as thermal tempering, or utilizing a mismatch of the coefficient ofthermal expansion between portions of the substrate to createcompressive stress and central tension regions, may be utilized to formstrengthened substrates.

Where the substrate is chemically strengthened by an ion exchangeprocess, the ions in the surface layer of the substrate are replacedby—or exchanged with—larger ions having the same valence or oxidationstate. Ion exchange processes are typically carried out by immersing asubstrate in a molten salt bath containing the larger ions to beexchanged with the smaller ions in the substrate. It will be appreciatedby those skilled in the art that parameters for the ion exchangeprocess, including, but not limited to, bath composition andtemperature, immersion time, the number of immersions of the substratein a salt bath (or baths), use of multiple salt baths, additional stepssuch as annealing, washing, and the like, are generally determined bythe composition of the substrate and the desired compressive stress(CS), depth of compressive stress layer (or depth of layer) of thesubstrate that result from the strengthening operation. By way ofexample, ion exchange of alkali metal-containing glass substrates may beachieved by immersion in at least one molten bath containing a salt suchas, but not limited to, nitrates, sulfates, and chlorides of the largeralkali metal ion. The temperature of the molten salt bath typically isin a range from about 380° C. up to about 450° C., while immersion timesrange from about 15 minutes up to about 40 hours. However, temperaturesand immersion times different from those described above may also beused.

In addition, non-limiting examples of ion exchange processes in whichglass substrates are immersed in multiple ion exchange baths, withwashing and/or annealing steps between immersions, are described in U.S.patent application Ser. No. 12/500,650, filed Jul. 10, 2009, by DouglasC. Allan et al., entitled “Glass with Compressive Surface for ConsumerApplications” and claiming priority from U.S. Provisional PatentApplication No. 61/079,995, filed Jul. 11, 2008, in which glasssubstrates are strengthened by immersion in multiple, successive, ionexchange treatments in salt baths of different concentrations; and U.S.Pat. No. 8,312,739, by Christopher M. Lee et al., issued on Nov. 20,2012, and entitled “Dual Stage Ion Exchange for Chemical Strengtheningof Glass,” and claiming priority from U.S. Provisional PatentApplication No. 61/084,398, filed Jul. 29, 2008, in which glasssubstrates are strengthened by ion exchange in a first bath is dilutedwith an effluent ion, followed by immersion in a second bath having asmaller concentration of the effluent ion than the first bath. Thecontents of U.S. patent application Ser. No. 12/500,650 and U.S. Pat.No. 8,312,739 are incorporated herein by reference in their entirety.

The degree of chemical strengthening achieved by ion exchange may bequantified based on the parameters of central tension (CT), surface CS,and depth of layer (DOL). Surface CS may be measured near the surface orwithin the strengthened glass at various depths. A maximum CS value mayinclude the measured CS at the surface (CS_(s)) of the strengthenedsubstrate. The CT, which is computed for the inner region adjacent thecompressive stress layer within a glass substrate, can be calculatedfrom the CS, the physical thickness t, and the DOL. CS and DOL aremeasured using those means known in the art. Such means include, but arenot limited to, measurement of surface stress (FSM) using commerciallyavailable instruments such as the FSM-6000, manufactured by Luceo Co.,Ltd. (Tokyo, Japan), or the like, and methods of measuring CS and DOLare described in ASTM 1422C-99, entitled “Standard Specification forChemically Strengthened Flat Glass,” and ASTM 1279.19779 “Standard TestMethod for Non-Destructive Photoelastic Measurement of Edge and SurfaceStresses in Annealed, Heat-Strengthened, and Fully-Tempered Flat Glass,”the contents of which are incorporated herein by reference in theirentirety. Surface stress measurements rely upon the accurate measurementof the stress optical coefficient (SOC), which is related to thebirefringence of the glass substrate. SOC in turn is measured by thosemethods that are known in the art, such as fiber and four point bendmethods, both of which are described in ASTM standard C770-98 (2008),entitled “Standard Test Method for Measurement of Glass Stress-OpticalCoefficient,” the contents of which are incorporated herein by referencein their entirety, and a bulk cylinder method. The relationship betweenCS and CT is given by the expression (1):

CT=(CS·DOL)/(t−2DOL)  (1),

wherein t is the physical thickness (μm) of the glass article. Invarious sections of the disclosure, CT and CS are expressed herein inmegaPascals (MPa), physical thickness t is expressed in eithermicrometers (μm) or millimeters (mm) and DOL is expressed in micrometers(μm).

In one embodiment, a strengthened substrate can have a surface CS of 250MPa or greater, 300 MPa or greater, e.g., 400 MPa or greater, 450 MPa orgreater, 500 MPa or greater, 550 MPa or greater, 600 MPa or greater, 650MPa or greater, 700 MPa or greater, 750 MPa or greater or 800 MPa orgreater. The strengthened substrate may have a DOL of 10 μm or greater,15 μm or greater, 20 μm or greater (e.g., 25 μm, 30 μm, 35 μm, 40 μm, 45μm, 50 μm or greater) and/or a CT of 10 MPa or greater, 20 MPa orgreater, 30 MPa or greater, 40 MPa or greater (e.g., 42 MPa, 45 MPa, or50 MPa or greater) but less than 100 MPa (e.g., 95, 90, 85, 80, 75, 70,65, 60, 55 MPa or less). In one or more specific embodiments, thestrengthened substrate has one or more of the following: a surface CSgreater than 500 MPa, a DOL greater than 15 μm, and a CT greater than 18MPa.

Example glasses that may be used in the substrate may include alkalialuminosilicate glass compositions or alkali aluminoborosilicate glasscompositions, though other glass compositions are contemplated. Suchglass compositions are capable of being chemically strengthened by anion exchange process. One example glass composition comprises SiO₂, B₂O₃and Na₂O, where (SiO₂+B₂O₃)≥66 mol. %, and Na₂O≥9 mol. %. In anembodiment, the glass composition includes at least 6 wt. % aluminumoxide. In a further embodiment, the substrate includes a glasscomposition with one or more alkaline earth oxides, such that a contentof alkaline earth oxides is at least 5 wt. %. Suitable glasscompositions, in some embodiments, further comprise at least one of K₂O,MgO, and CaO. In a particular embodiment, the glass compositions used inthe substrate can comprise 61-75 mol. % SiO₂; 7-15 mol. % Al₂O₃; 0-12mol. % B₂O₃; 9-21 mol. % Na₂O; 0-4 mol. % K₂O; 0-7 mol. % MgO; and 0-3mol. % CaO.

A further example glass composition suitable for the substratecomprises: 60-70 mol. % SiO₂; 6-14 mol. % Al₂O₃; 0-15 mol. % B₂O₃; 0-15mol. % Li₂O; 0-20 mol. % Na₂O; 0-10 mol. % K₂O; 0-8 mol. % MgO; 0-10mol. % CaO; 0-5 mol. % ZrO₂; 0-1 mol. % SnO₂; 0-1 mol. % CeO₂; less than50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; where 12 mol. %(Li₂O+Na₂O+K₂O) 20 mol. % and 0 mol. %≤(MgO+CaO)≤10 mol. %.

A still further example glass composition suitable for the substratecomprises: 63.5-66.5 mol. % SiO₂; 8-12 mol. % Al₂O₃; 0-3 mol. % B₂O₃;0-5 mol. % Li₂O 8-18 mol. % Na₂O; 0-5 mol. % K₂O; 1-7 mol. % MgO; 0-2.5mol. % CaO; 0-3 mol. % ZrO₂; 0.05-0.25 mol. % SnO₂; 0.05-0.5 mol. %CeO₂; less than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; where 14 mol.%≤(Li₂O+Na₂O+K₂O)≤18 mol. % and 2 mol. %≤(MgO+CaO)≤7 mol. %.

In a particular embodiment, an alkali aluminosilicate glass compositionsuitable for the substrate comprises alumina, at least one alkali metaland, in some embodiments, greater than 50 mol. % SiO₂, in otherembodiments at least 58 mol. % SiO₂, and in still other embodiments atleast 60 mol. % SiO₂, wherein the ratio

${\frac{{{Al}_{2}O_{3}} + {B_{2}O_{3}}}{\sum{modifiers}} > 1},$

where in the ratio the components are expressed in mol. % and themodifiers are alkali metal oxides. This glass composition, in particularembodiments, comprises: 58-72 mol. % SiO₂; 9-17 mol. % Al₂O₃; 2-12 mol.% B₂O₃; 8-16 mol. % Na₂O; and 0-4 mol. % K₂O, wherein the ratio

${\frac{{{Al}_{2}O_{3}} + {B_{2}O_{3}}}{\sum{modifiers}} > 1}.$

In still another embodiment, the substrate may include an alkalialuminosilicate glass composition comprising: 64-68 mol. % SiO₂; 12-16mol. % Na₂O; 8-12 mol. % Al₂O₃; 0-3 mol. % B₂O₃; 2-5 mol. % K₂O; 4-6mol. % MgO; and 0-5 mol. % CaO, wherein: 66 mol. %≤SiO₂+B₂O₃+CaO≤69 mol.%; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO>10 mol. %; 5 mol. %≤MgO+CaO+SrO≤8 mol. %;(Na₂O+B₂O₃)−Al₂O₃≤2 mol. %; 2 mol. %≤Na₂O−Al₂O₃≤6 mol. %; and 4 mol.%≤(Na₂O+K₂O)−Al₂O₃≤10 mol. %.

In an alternative embodiment, the substrate may comprise an alkalialuminosilicate glass composition comprising: 2 mol % or more of Al₂O₃and/or ZrO₂, or 4 mol % or more of Al₂O₃ and/or ZrO₂.

Where the substrate includes a crystalline substrate, the substrate mayinclude a single crystal, which may include Al₂O₃. Such single crystalsubstrates are referred to as sapphire. Other suitable materials for acrystalline substrate include polycrystalline alumina layer and/orspinel (MgAl₂O₄).

Optionally, the crystalline substrate may include a glass ceramicsubstrate, which may be strengthened or non-strengthened. Examples ofsuitable glass ceramics may include Li₂O—Al₂O₃—SiO₂ system (i.e.LAS-System) glass ceramics, MgO—Al₂O₃—SiO₂ system (i.e. MAS-System)glass ceramics, and/or glass ceramics that include a predominant crystalphase including β-quartz solid solution, β-spodumene ss, cordierite, andlithium disilicate. The glass ceramic substrates may be strengthenedusing the chemical strengthening processes disclosed herein. In one ormore embodiments, MAS-System glass ceramic substrates may bestrengthened in Li₂SO₄ molten salt, whereby an exchange of 2Li⁺ for Mg²⁺can occur.

The substrate according to one or more embodiments can have a physicalthickness ranging from about 100 μm to about 5 mm. Example substratephysical thicknesses range from about 100 μm to about 500 μm (e.g., 100,200, 300, 400 or 500 μm). Further example substrate physical thicknessesrange from about 500 μm to about 1000 μm (e.g., 500, 600, 700, 800, 900or 1000 μm). The substrate may have a physical thickness greater thanabout 1 mm (e.g., about 2, 3, 4, or 5 mm). In one or more specificembodiments, the substrate may have a physical thickness of 2 mm or lessor less than 1 mm. The substrate may be acid polished or otherwisetreated to remove or reduce the effect of surface flaws.

Examples of articles that may include such anti-glare substrates includedisplays used in electronic devices such as laptops, mobile phones,smart phones, tablets, electronic readers, point of sale devices,inventory devices, navigation systems, automotive dashboards, automotiveconsoles, appliances (e.g., stoves, ranges, dishwashers, andrefrigerators). The anti-glare substrates described herein may also beused in the housings of such electronic devices for decorative purposes.The anti-glare substrates may also be incorporated into architecturalarticles such as countertops, windows, elevators and the like).

A second aspect of this disclosure pertains to methods of forming theanti-glare substrates described herein. In one or more embodiments, themethod includes providing a substrate having a surface and etching aportion of the surface to provide an etched surface and removing aportion of the etched surface to provide an anti-glare surface or atextured surface, as described herein.

In one or more embodiments, the etchant exhibits lower water solubilitythan known etchants. For example, in some embodiments, the etchantexhibits a water solubility of about 50 g/100 g water or less (e.g.,about 40 g/100 g water or less, or about 30 g/100 g water or less). Insome examples, the etchant includes a potassium salt and exhibits awater solubility of about 39.2 g/100 g water. The potassium salt mayinclude KCl, soluble inorganic potassium salts (e.g., KNO₃, K₂SO₄ orcombinations thereof), water-soluble organic salts (e.g., potassiumacetate) and combinations thereof. In one or more specific embodiments,the etchant may have the composition KHF₂ or may include a combinationof salts, which together have active components including potassiumions, fluoride ions and a low pH.

The etchant may include potassium salt in an amount in the range fromabout 0.1 wt % to about 20 wt %, from about 0.1 wt % to about 18 wt %,from about 0.1 wt % to about 16 wt %, from about 0.1 wt % to about 14 wt%, from about 0.1 wt % to about 12 wt %, from about 1 wt % to about 20wt %, from about 2 wt % to about 20 wt %, from about 4 wt % to about 20wt %, from about 6 wt % to about 20 wt %, from about 8 wt % to about 20wt % from about 10 wt % to about 20 wt % from about 12 wt % to about 20wt %, from about 5 wt % to about 15 wt % or from about 5 wt % to about10 wt %.

In some embodiments, when the concentration of the potassium salt isless than about 5 wt % (e.g. about 2 wt %), the precipitate formation isinsufficient and the desired textured surface cannot be formed. In someembodiments, when the potassium salt concentration is greater than about10 wt %, the etchant is less uniform. In one or more embodiments, theetchant includes KCl in an amount in the range from about 5 wt % toabout 10 wt %.

In some embodiments, the etchant includes a fluoride containing acid.The fluoride containing acid may be present in an amount in the rangefrom about 0.5 wt % to about 6 wt %, from about 1 wt % to about 6 wt %,or from about 1 wt % to about 3 wt %. Examples of suitable fluoridecontaining acids include hydrofluoric acid (HF) and ammonium bifluoride(NH₄HF₂). Without being bound by theory, and as described more fullybelow, the fluoride containing acid etches the substrate and generates aprecipitate of insoluble crystals including SiF₆ ²⁻ ions by forming ionsof the precipitate on the surface of the substrate. When theconcentration of the fluoride containing acid is less than about 1 wt %or less than about 0.5 wt %, the etch rate is significantly reduced andthe etchant cannot generate sufficient SiF₆ ²⁻ ions to form crystals.This results in a textured surface that that has reduced surfaceroughness, low PPDr values, and DOI values approaching 100. When thefluoride containing acid concentration in the etchant is greater thanabout 6 wt %, the desirable textured surface also cannot be achievedbecause the etchant removes the insoluble crystals without forming thedesired textured surface. Accordingly, in some embodiments, the etchantincludes HF as the fluoride containing acid in an amount in the rangefrom about 1 wt % to about 3 wt %.

The etchant may include an organic solvent. The organic solvent may bepresent in the etchant in an amount in the range from about 0 wt % toabout 40 wt %, from about 1 wt % to about 40 wt %, from about 5 wt % toabout 40 wt %, from about 10 wt % to about 40 wt %, from about 1 wt % toabout 35 wt %, from about 1 wt % to about 30 wt %, from about 1 wt % toabout 25 wt %, or from about 10 wt % to about 25 wt %. Examples ofsuitable organic solvents include one or more of propylene glycol,acetic acid, ethanol, propanol, and other solvents miscible in water.

In some instances, the etchant may be substantially free of ammoniumsalt. As used herein, the phrase “substantially free” means notintentionally added or present in an amount of less than about 0.01 wt%.

The etchant may have a viscosity enabling spray application of theetchant on the surface of the substrate.

In one or more embodiments, the method includes generating a precipitateon the surface of the substrate on which the etchant is applied andforming an etched surface. In some embodiments, the method includesdisposing or maintaining the etchant on the surface until a sufficientnumber and size of precipitates are formed and the desired etchedsurface is formed. In other words, the application of an etchantincludes an in situ precipitate formation (forming a precipitate or maskon the surface of the substrate) and etching process, by which thepattern of the precipitate or mask is transferred onto the surface ofthe substrate.

In one or more embodiments, the method includes applying the etchant andleaving it on the surface for a duration of up to and including about 20minutes, up to and including about 18 minutes, up to and including about16 minutes, up to and including about 14, up to and including about 12minutes, up to and including about 10 minutes, up to and including about8 minutes, up to and including about 6 minutes, up to and includingabout 5 minutes, or up to and including about 4 minutes.

The precipitate or mask may include a plurality of insoluble crystals.In one or more embodiments, the plurality of insoluble crystals aredensely packed or disposed on the surface in a dense configuration(e.g., with limited, minimized or no space between the crystals). In oneor more embodiments, the crystals should have an average cross-sectionaldimensionin the range from about 1 micrometer to about 10 micrometers.In some embodiments, the insoluble crystals exhibit a water solubilityof less than about 10 g/100 g or water (e.g., about 1 g/100 g of wateror less, or about 0.1 g/100 g of water or less). The insoluble crystalsmay include potassium and may comprise any one or more of K₂SiF₆ andK₃AlF₆. In such embodiments, the water solubility of thepotassium-containing insoluble crystals may be about 0.084 g/100 gwater.

When compared to known, ammonium-containing etchants that utilize NH₄ ⁺cations (e.g., etchants such as NH₄F, NH₄HF₂ and/or other ammoniumsalts), the etchants described herein utilize potassium salt and K⁺cations to generate insoluble crystals on the substrate surface, asillustrated by Equations 4 and 6. Equations 4 and 5 illustrate thegeneration of a precipitate having greater water solubility, using knownammonium-containing etchants that utilize NH₄ ⁺ cations.

SiO₂+6HF→SiF₆ ²⁻+2H₂O+2H⁺  (4)

2NH₄ ⁺+SiF₆ ²⁻→(NH₄)₂SiF₆(insoluble)↓  (5)

2K⁺++SiF₆ ²⁻→K₂SiF₆(insoluble)↓  (6)

The insoluble crystals including potassium (and generated using theetchants of one or more embodiments of this disclosure) exhibit muchlower water solubility than the known precipitates (such as ammoniumprecipitates generated using known ammonium-containing etchants).Specifically, the insoluble crystals generated by the etchant of one ormore embodiments of this disclosure include K₂SiF₆, which exhibit awater solubility of about 0.084 g/100 g water; whereas knownammonium-containing etchants that utilize NH₄ ⁺ cations generatecrystals such as (NH₄)₂SiF₆, which exhibit a water solubility of about22.7 g/100 g water, as shown in Table 1. Without being bound by theory,it is believed that reducing the water solubility of precipitatesprovides an anti-glare surface exhibiting reduced sparkle.

TABLE 1 Comparison of a known ammonium-based etchant that utilize NH₄ ⁺cations and etchants according to one or more embodiments of thisdisclosure. Etchant Precipitate Cation solubility solubility of Etchant(g/100 g (g/100 g Etchant etchant formula water) Precipitate water)Comparative NH₄ ⁺ NH₄HF₂ 60.2 (NH₄)₂SiF₆ 22.7 Potassium K⁺ KHF₂ 39.2K₂SiF₆ 0.084 based etchant

Due to the lower water solubility exhibited by the potassium crystals, agreater number of crystals can be generated from the etchants describedherein. FIGS. 2A and 2B illustrate the generation and growth of thecrystals according to one or more embodiments of this disclosure and thegeneration and growth of crystals according to known methods thatutilize an ammonium-based etchant (which in turn, utilizes NH₄ ⁺cations). As shown in FIGS. 2A and 2B, the number of the crystals onsubstrate surface can influence the maximum size of the crystals and thesize of the surface features on the resulting anti-glare surface. Forillustration, a glass substrate 100 is utilized; however, it is notedthat the substrate may include a crystalline substrate. Referring toFIG. 2A, the application of the etchant of one or more embodiments ofthis disclosure (10A) forms more crystals 220 on glass surface 112,which grow (11A) but remain relatively small in size, and providesmaller spaces between the crystals 230. Without being bound by theory,it is believed that the lower water solubility of the crystals 220(specifically, crystals that include K₂SiF₆) enables the rapid formationof crystal seeds at a higher density. The crystal seeds grow larger butonly to limited sizes due to the higher density of the crystal seeds.When the etchant of one or more embodiments is removed and a portion ofthe surface 112 of the glass is removed (12A), the resulting anti-glaresurface has features 240 having a smaller size (i.e., having a size thatcorresponds to the size of the spaces between the crystals 230). Thesmaller features 240 provide an anti-glare surface that exhibits lowsparkle.

For comparison and referring to FIG. 2B, the application of a knownammonium-based etchant that utilizes NH₄ ⁺ cations (10B) forms fewercrystals 320 on the surface of the glass 112 and their growth (11B) isunlimited (due to fewer crystals on the surface). The resulting crystalsize is larger and thus larger spaces are formed between the crystals330. When the known etchant is removed and a portion of the surface 112of the glass substrate is removed (12B), the resulting anti-glaresurface has features 340 with larger sizes (i.e., having a size thatcorresponds to the size of the space between the crystals 23). Thelarger features 340 provide an anti-glare surface that exhibit greatersparkle.

Without being bound by theory, it is believed the use of a propyleneglycol organic solvent further reduces the water solubility of thepotassium crystals, and facilitates the generation of more crystals(formed at 10A in FIG. 2A). Moreover, propylene glycol is also believedto reduce the feature size and thus the sparkle exhibited by theresulting anti-glare surface.

In some embodiments, the etchant may include a small amount of ammoniumfluoride (NH₄F). Without being bound by theory, such other salts do notsignificantly influence the formation of small crystals by potassiumsalts. In yet other embodiments, the etchant may include an insolubleparticle or particles and optionally, a surfactant.

The method includes removing the etchant and precipitate after a desiredamount and/or concentration of insoluble crystals are formed or adesired average size and size distribution of insoluble crystals areformed. The etchant may be removed by exposing the etchant to a cleaningsolution and rinsing with DI water. In some embodiments, the cleaningsolution may include H₂SO₄ having a concentration of about 10 wt % orless (e.g., about 8 wt % or less, about 6 wt % or less, about 5 wt % orless, about 4 wt % or less, or about 3 wt % or less). The etchant may beexposed to the cleaning solution for a duration of time sufficient toremove the etchant and the precipitate (or insoluble crystals) (e.g.,about 10 minutes or less, about 8 minutes or less, about 6 minutes orless, about 5 minutes or less or about 4 minutes or less). The removalof the etchant and precipitate removes portions of the surface that donot include any insoluble crystals, forming an etched surface havingsmall features (i.e., 140, FIG. 2A).

In some embodiments, the method includes removing a portion of theetched surface using a chemical polishing solution or other means knownin the art to provide an anti-glare surface exhibiting the low sparkle,low DOI and low transmission haze, described herein. Specifically, theetched surface or a portion thereof is exposed to the chemical polishingsolution for a duration of time to remove a portion of the etchedsurface. In some embodiments, a surface thickness of up to about 100micrometers of the etched surface may be removed. In some instances,about 40 micrometers to about 100 micrometers of the etched surface maybe removed. The removal may be controlled by the concentration of thechemical polishing solution or the exposure time of the etched surfaceto the chemical polishing solution. The chemical polishing solution mayinclude hydrofluoric acid, a mineral acid (e.g., hydrochloric acid(HCl), and H₂SO₄), or a combination thereof.

In one or more embodiments, the etchants described herein can provide asubstrate with a textured surface that exhibits desirable PPDr and DOIvalues, which can be tuned by varying the concentrations of thecomponents of the etchant, within the ranges provided herein. Forexample, the resulting substrates according to one or more embodimentsmay exhibit a transmission haze of about 10%, a PPDr value in the rangefrom about 4.5 to 7, and DOI value from in the range from about 30 toabout 100, as shown in FIGS. 3 and 4. As shown in FIGS. 3 and 4, reducedconcentrations of the organic solvent can reduce DOI but could increasePPDr. Moreover, variations in the fluoride-containing acid could alsoinfluence PPDr and DOI values. However, the embodiments disclosed hereinexhibit optimized combinations of transmission haze, PPDr and DOI. Asshown in FIG. 3, when the concentration of the fluoride-containing acid(HF) is less than about 1 wt %, the substrate may not be sufficientlytextured and the DOI value tends to be high (e.g., close to 100%);however, the PPDr value may be between 2-4.5%. When the concentration ofthe fluoride-containing acid (HF) is in the range from about 1 wt % toabout 3 wt %, increasing the concentration of the organic solventreduces PPDr value, and increases the DOI value. As specifically shownin FIG. 4, when the organic solvent concentration is greater than about10 wt %, varying the potassium salt (KCl) concentration from about 5 wt% to about 10 wt % does not significantly influence the correlation ofPPDr and DOI of the substrate. When the organic solvent concentration isless than about 10 wt %, decreasing the potassium salt (KCl)concentration can reduce the PPDr value.

In one or more embodiments, the method may include applying a coating onthe textured surface. In some instances, reflection from the anti-glaresurface may be reduced by application of an anti-reflective coating onthe surface. In other embodiments, scratch-resistance may be imparted tothe textured surface by applying a scratch-resistant coating on thesurface.

Prior to, during and after the formation of the textured surface, asdescribed herein, the substrate may be cleaned using various knowncleaning solutions and methods (e.g., in-line cleaning, acid etchingetc.).

EXAMPLES

Various embodiments will be further clarified by the following examples.

Example 1

In Example 1, a glass substrate having a nominal composition of about 69mol % SiO₂, 8.5 mol % Al₂O₃, 14 mol % Na₂O, 1.2 mol % K₂O, 6.5 mol % MgOand 0.5 mol % CaO, and about 0.2 mol % SnO₂, was cleaned using acleaning solution including about 2.5 wt % hydrofluoric acid and 1.8 wt% hydrochloric acid for about 1 minute. The cleaned glass was rinsed inDI water and then a major surface of the substrate was exposed to anetchant for 8 minutes to form an etched surface. The etchant includedabout 1 wt % HF, 10 wt % KCl, and 25 wt % propylene glycol. The etchedsurface was then cleaned by soaking the substrate in a solution of 5.3wt % H₂SO₄ for 5 minutes and then rinsed with DI water. The etchedsurface was then chemically polished to different depths (or untilspecific thicknesses of the etched surface are removed) using a chemicalpolishing solution of 2.5 wt % HF and 1.8 wt % HCl, as shown in Table 2.The properties of the resulting textured surface.

TABLE 2 Properties of Example 1, after removal of specific thicknessesof the etched surface. Thickness of Surface etched surface T-Haze PPDrGloss Roughness removed (μm) (%) DOI (%) (60°) (Ra, nm) 0 46.5 91.3 3.2819.1 186.5 4 56.7 0 3.77 15.8 284.0 12 32.3 62.2 4.1 260.5 25 20.9 74.54.74 32.7 190.7 40 16.2 82.4 4.97 41 163.1 60 9.73 81.8 4.62 51 141.7100 6.11 84.9 5.29 68.8 114.0

As shown in Table 2, after removal of about 60 micrometers of the etchedsurface, the substrate exhibited a T-haze of about 10%, a PPDr value ofabout 4. And a DOI of about 826. After removal of about 100 micrometersof the etched surface, the substrate exhibited a T-haze level of about6%, a PPDr value of about 5.3% and a DOI of about 85.

FIG. 5 is an image of the etched surface, taken at 200× magnification,using an optical microscope, supplied by Nikon. FIG. 6 is an image ofthe textured surface after chemical polishing and removal of about 100micrometers of the etched surface, taken at 200× magnification using thesame optical microscope. The scale bar shown in FIGS. 3 and 4 is for 100micrometers. In FIG. 6, the features were selected for measurement oftheir respective cross-sectional dimensions, as defined herein, and theaverage cross-sectional dimension was calculated (based on themeasurements of 20 different features) to about 22 micrometers.

Example 2

Example 2 utilized the same glass substrate as Example 1. The substratewas cleaned using the same cleaning solution and method as used inExample 1. The cleaned glass was rinsed in DI water and then a majorsurface of the substrate was exposed to an etchant for 8 minutes to forman etched surface. The etchant included about 1 wt % HF, 5 wt % KCl, and25 wt % propylene glycol. The etched surface was then cleaned by soakingthe substrate in a solution of 5.3 wt % H₂SO₄ for 5 minutes and thenrinsed with DI water. The etched surface was then chemically polished todifferent depths (or until specific thicknesses of the etched surfaceare removed) using the same chemical polishing solution used in Example1, as shown in Table 3. The properties of the resulting texturedsurface.

TABLE 3 Properties of Example 2, after removal of specific thicknessesof the etched surface. Thickness of etched surface T-Haze PPDr Glossremoved (μm) (%) DOI (%) (60°) 0 37.8 89.2 3.36 20.1 4 47 65.8 3.86 18.312 30.4 58 4.38 5 20.3 68.1 4.67 31.6 40 15.6 71.1 5.18 37.2 60 10.476.7 5.14 46.8 100 8.27 77.4 5.37 57.6

As shown in Table 3, after removal of about 60 micrometers of the etchedsurface, the substrate exhibited a T-haze level of about 10%, a PPDrvalue of about 5.1 and a DOI of less than about 77. After removal ofabout 100 micrometers of the etched surface, the substrate exhibited aT-haze level of about 8%, a PPDr value of about 5 and a DOI of about 77.The average cross-sectional dimension of the features of the resultingtextured surface was about 23 micrometers.

Example 3

Example 3 utilized the same glass substrate as Example 1. The substratewas cleaned using the same cleaning solution and method as used inExample 1. The cleaned glass was rinsed in DI water and then a majorsurface of the substrate was exposed to an etchant for 8 minutes to forman etched surface. The etchant included about 6 wt % HF, 15 wt % KCl.The etchant did not include an organic solvent or, more specifically,propylene glycol. The etched surface was then cleaned by soaking thesubstrate in a solution of 5.3 wt % H₂SO₄ for 5 minutes and then rinsedwith DI water. The etched surface was then chemically polished todifferent depths (or until specific thicknesses of the etched surfaceare removed) using the same chemical polishing solution used in Example1, as shown in Table 4. The properties of the resulting texturedsurface.

TABLE 4 Properties of Example 3, after removal of specific thicknessesof the etched surface. Thickness of etched surface T-Haze Gloss removed(μm) (%) DOI PPDr (60°) 0 30.2 39 4 47.8 37.5 4.69 20.4 12 36.8 0 4.5125 29.6 28.2 4.88 25.7 40 23 30.7 5.64 30.8 60 16.7 31.5 6.4 37 100 8.8833.3 8.4 48

As shown in Table 4, after removal of about 60 micrometers of the etchedsurface, the substrate exhibited a T-haze level of about 17%, a PPDrvalue of about 6.4 and a DOI of less than about 32. After removal ofabout 100 micrometers of the etched surface, the substrate exhibited aT-haze level of about 8.9%, a PPDr value of about 8.44 and a DOI ofabout 33. The average cross-sectional dimension of the features of theresulting textured surface was about 33 micrometers.

Example 4

Example 4 utilized a glass substrate having a nominal composition ofabout 65 mol % SiO₂, 5 mol % B₂O₃, 14 mol % Al₂O₃, 14 mol % Na₂O, 2.4mol % MgO, and about 0.08 mol % SnO₂. The substrate was cleaned usingthe same cleaning solution and method as used in Example 1. The cleanedglass was rinsed in DI water and then a major surface of the substratewas exposed to an etchant for 8 minutes to form an etched surface. Theetchant included about 6 wt % HF, 10 wt % KCl, and 25 wt % of propyleneglycol. The etched surface was then cleaned by soaking the substrate ina solution of 5.3 wt % H₂SO₄ for 5 minutes and then rinsed with DIwater. The etched surface was then chemically polished to differentdepths (or until specific thicknesses of the etched surface are removed)using the same chemical polishing solution used in Example 1, as shownin Table 5. The properties of the resulting textured surface.

TABLE 5 Properties of Example 4, after removal of specific thicknessesof the etched surface. Thickness of etched surface T-Haze PPDr Glossremoved (μm) (%) DOI (%) (60°) 0 65.2 93.9 3.82 12.8 20 26.7 88.1 4.5532.0 40 13.3 90.3 5.16 54.4 60 8.6 88.7 5.56 71.1 100 4.6 92.3 5.88 91.6

As shown in Table 5, after removal of about 60 micrometers of the etchedsurface, the substrate exhibited a T-haze level of about 8.6%, a PPDrvalue of about 5.56 and a DOI of less than about 88.7. After removal ofabout 100 micrometers of the etched surface, the substrate exhibited aT-haze level of about 4.6%, a PPDr value of about 5.88 and a DOI ofabout 92.3. The average cross-sectional dimension of the features of theresulting textured surface was about 20 micrometers.

Example 5

Example 5 utilized the same glass substrate as Example 4, which wascleaned using the same cleaning solution and method as used inExample 1. The cleaned glass was rinsed in DI water and then a majorsurface of the substrate was exposed to an etchant for 16 minutes toform an etched surface. The etchant included about 1 wt % HF, 10 wt %KCl, and 25 wt % of propylene glycol. The etched surface was thencleaned by soaking the substrate in a solution of 5.3 wt % H₂SO₄ for 5minutes and then rinsed with DI water. The etched surface was thenchemically polished to different depths (or until specific thicknessesof the etched surface are removed) using the same chemical polishingsolution used in Example 1, as shown in Table 6. The properties of theresulting textured surface.

TABLE 6 Properties of Example 5, after removal of specific thicknessesof the etched surface. Thickness of etched surface T-Haze PPDr Glossremoved (μm) (%) DOI (%) (60°) 0 64.6 93.8 3.75 3.5 20 26.0 88.4 4.4932.0 40 13.9 91.1 4.93 54.4 60 8.8 89.7 5.38 71.1 100 4.3 91.6 5.72 86.6

As shown in Table 6, after removal of about 60 micrometers of the etchedsurface, the substrate exhibited a T-haze level of about 8.8%, a PPDrvalue of about 5.38 and a DOI of less than about 89.7. After removal ofabout 100 micrometers of the etched surface, the substrate exhibited aT-haze level of about 4.3%, a PPDr value of about 5.72 and a DOI ofabout 91.6. The average cross-sectional dimension of the features of theresulting textured surface was about 20 micrometers.

Example 6

Examples 6A-6R included the same glass substrate as Examples 4 and 5(“Substrate 1”) and were prepared using the conditions shown below inTable 7. The DOI, PPDr and transmission haze was measured at differentchemical polishing depths. The calculated DOI and PPDr values based on atransmission haze of 10% are shown in Table 8.

TABLE 7 Etchant composition, and measured DOI, PPDr and transmissionhaze values at different chemical polishing depths for Examples 6A-6R.Etchant for glass DOI (%) at chemical polishing PPDr (%) at chemicalHaze (%)at chemical roughening (wt %) depths (μm) polishing depths (μm)polishing depths (μm) Ex. HF PG KCl 0 20 50 100 0 20 50 100 0 20 50 1006A 0.5 0 10 97.5 99.2 100 100 6.0 2.8 2.6 2.0 24.5 3.7 1.4 0.3 6B 0.5 510 100 99.6 99.6 99.6 1.9 0.8 1.8 1.8 0.1 0.1 0.1 0.1 6C 0.5 15 10 97.699.3 99.5 99.1 6.1 2.3 1.9 2.0 28.8 2.4 0.5 0.2 6D 0.5 25 10 96.3 99.599.6 99.7 5.0 1.5 1.8 1.9 56.2 2.6 0.6 0.2 6E 1 15 5 74.3 24.5 55.2 79.43.5 3.9 5.4 6.6 73.1 46.5 17.8 5.7 6F 1 0 10 64.6 88.2 96.3 98.5 4.6 3.63.5 2.2 83.7 39.6 9.2 2.1 6G 1 5 10 0.0 4.3 2.2 30.5 4.1 3.6 5.1 6.786.3 71.2 39.8 9.2 6H 1 15 10 0.0 52.3 55.1 54.3 4.5 4.0 4.2 7.1 85.247.3 26.1 5.7 6I 1 25 10 93.8 88.4 89.7 91.6 3.8 4.5 5.4 5.7 64.6 26 8.84.3 6J 3 0 5 30.0 10.9 10.0 6K 3 5 5 76.8 7.1 35.5 65.4 4.0 4.1 5.3 6.942.0 44.4 17.7 5.6 6L 3 10 5 95.3 58.6 79.5 87.4 3.5 4.4 5.4 6.4 29.334.3 13.6 4.3 6M 3 15 5 98.1 93 93.6 94.4 2.9 4.1 4.4 4.5 16.6 19.5 8.12.8 6N 3 25 5 97.7 2.0 8.6 6O 3 0 10 94.7 17.3 43.3 70.7 3.7 3.9 5.3 7.958.7 60.5 25.2 6.8 6P 3 5 10 93.8 23.6 70.3 74.1 3.5 3.9 5.7 7.4 51.646.6 16.1 5.4 6Q 3 15 10 97.9 93.8 94.3 94.6 3.0 4.0 4.9 5.5 35.2 25.68.8 3.0 6R 3 25 10 98.0 2.0 11.6

TABLE 8 Calculated DOI and PPDr values for Examples 6A-6R. CalculatedDOI (%) Calculated PPDr (%) Ex. Input Haze at 10% Haze at 10% Haze 6A10.0 99.0 4.3 6B 10.0 99.0 1.8 6C 10.0 99.0 3.4 6D 10.0 99.0 2.2 6E 10.070.0 6.1 6F 10.0 96.2 3.5 6G 10.0 29.4 6.6 6H 10.0 54.7 6.1 6I 10.0 90.35.2 6J 10.0 30.0 10.9 6K 10.0 49.9 6.1 6L 10.0 82.3 5.8 6M 10.0 93.7 4.46N 10.0 97.7 2.0 6O 10.0 65.2 7.1 6P 10.0 73.3 6.4 6Q 10.0 94.3 4.7 6R10.0 98.0 2.0

The calculated DOI and PPDr values at transmission haze of 10% wereplotted in FIG. 7. For comparison, substrates having the samecomposition as Substrate 1 or the same composition as the substratesused in Examples 1-3 (“Substrate 2”) were subjected to known methods offorming a textured surface. The PPDr and DOI values at a transmissionhaze of about 10% of those comparative substrates are also shown in FIG.7. The shaded portion of the graph of FIG. 7 (including solid circles)are collected data points (i.e., PPDr and DOI) from Table 8. ComparativeExample 6S are substrates formed using a comparative cream (or sludge)etching process. Comparative Examples 6T and 6V represent substratesformed using an ammonium-salt based etchant. Comparative Example 6Urepresents substrates formed using a sand blasting and etchingtechnique. Comparative Example 6W represents substrates formed using asol-gel process.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention.

1-47. (canceled)
 48. An article comprising: a substrate; and at leastone textured surface comprising a plurality of features having anaverage cross-sectional dimension of about 30 micrometers or less,wherein the article exhibits a transmission haze of 10% or less, a pixelpower deviation PPDr of about 7% or less and a distinctiveness of imageDOI of about 80 or less.
 49. The article of claim 48, wherein the PPDrvalue is about 6% or less.
 50. The article of claim 48, wherein thefeatures comprise a Rsk value in the range from about 1 to about −1. 51.The article of claim 48, wherein the substrate comprises an amorphoussubstrate.
 52. The article of claim 51, wherein the amorphous substratecomprises a glass, and the glass is chemically strengthened andcomprises a compressive stress layer with a surface compressive stressof at least 250 MPa extending within the chemically strengthened glassfrom a surface of the glass to a depth of layer DOL of about 10 μm orgreater.
 53. The article of claim 49, wherein the features compriseconcave openings that face outwardly from the textured surface.
 54. Thearticle of claim 48, wherein the substrate comprises a crystallinesubstrate.
 55. The article of claim 51, wherein the amorphous substratecomprises a glass selected from the group consisting of soda lime glass,alkali aluminosilicate glass, alkali containing borosilicate glass andalkali aluminoborosilicate glass.
 56. The article of claim 48, whereinthe features comprise concave openings that face outwardly from thetextured surface.
 57. The article of claim 51, wherein the amorphoussubstrate comprises a glass, and the glass is chemically strengthenedand comprises a surface compressive stress of at least 250 MPa.
 58. Thearticle of claim 51, wherein the amorphous substrate comprises a glass,and the glass is chemically strengthened and comprises a compressivestress layer extending within the chemically strengthened glass from asurface of the glass to a depth of layer DOL of about 10 μm or greater.